A hybrid fiber-coaxial (HFC) network generally consists of three parts, a fiber backbone, a coaxial branch cable, and a user distribution network. A program signal from a cable television station is first converted into an optical signal for transmission over a fiber backbone. The optical signal is converted into an electrical signal in a user area, and the electrical signal is transmitted to users over a coaxial cable after being distributed by a distributor.
A typical HFC network includes devices such as a cable modem termination system (CMTS), a cable modem (CM), and an optical station, components (an amplifier, an attenuator, a splitter, and a distributor), an optical cable (fiber), a coaxial cable, and the like. A problem may occur on any device or component, or any section of cable on the HFC network. Therefore, an uplink signal on the HFC network is subject to various linear distortions such as a group delay and micro-reflection.
Data Over Cable Service Interface Specification (DOCSIS) 3.0 defines a pre-equalizer, where each CM has a pre-equalizer inside such that reverse compensation can be obtained for a signal before the CM transmits the signal. The pre-equalizer defined in DOCSIS 3.0 is a linear filter with 24 tap coefficients, where the 24 coefficients are referred to as pre-equalization coefficients. In a processing structure of the pre-equalizer, a delay of each tap coefficient is one symbol, and each of the tap coefficients has a different amplitude.
The pre-equalizer can temporarily relieve a distortion on a line in terms of data processing, but the fault (for example, cable impairment) still exists in the line. User service experience is affected when the fault becomes serious to some extent. Therefore, it is quite necessary to perform network operation and maintenance on a fault (especially a small fault) that occurs on a line.
Conventional network operation and maintenance is triggered in response to user complaints and is passive. Therefore, to better handle, locate, and troubleshoot a fault, proactive network maintenance (PNM) needs to be performed. It can be learnt from the foregoing that, a pre-equalizer is used to compensate for a distortion on a cable line, and a frequency domain response of the pre-equalizer is reversely complementary to a channel response of the line. Therefore, pre-equalization coefficients include line fault information. The pre-equalization coefficients may be used for analysis in order to discover a fault on a cable network in advance and locate the fault. This method for failure diagnosis by monitoring pre-equalization coefficients of each CM is referred to as PNM using Pre-equalization (PNMP).
In PNMP, algorithm analysis is performed according to pre-equalization coefficients. For example, parameters such as time domain tap coefficients and a frequency domain response may be obtained according to pre-equalization coefficients, for failure analysis. However, a means of performing failure analysis according to pre-equalization coefficients is relatively single. As a result, parameters obtained by means of calculation cannot reflect an actual status of a physical line accurately and thoroughly, which causes inaccurate failure analysis.